Process development for antifungal production by Bacillus subtilis BS20: nanoparticle supplementation, process optimization and preliminary scale-up studies

The intensive agricultural practices used to meet global crop production demands have resulted in rigorous use of chemical pesticides. These ultimately compromise crop production as well as the environment. To alleviate these challenges, cheaper and environmentally friendly biocontrol agents have been considered as an alternative to chemical pesticides. Hence, this study was undertaken with the aim of enhancing antifungal production by Bacillus subtilis BS20 through process modeling, optimization, nanocatalysis and subsequent assessment of the scale up potential of the optimized process. The investigated process parameters included glucose concentration (10-30 g/L), incubation temperature (25-45 ℃) and incubation time (24-96 h). Optimized process conditions of 11.5 g/L glucose concentration, 24 h incubation time and 41 °C incubation temperature produced maximal antifungal activity of 68 mm zone of inhibition. Moreover, the inclusion of nanoparticles favored increased biomass yield but low antifungal activity. Additionally, constant power consumption, Reynolds number (Re) and impeller tip (V_tip) speed were implemented to scale up the antifungal production by B. subtilis BS20. Implementing constant V_tip value from the 1 L scale: 93 rpm, Re = 5.9E-04, Power (P) = 0.32 W, Power to Volume ratio (P/V_L) = 160 W/m³, circulation time (t_c) = 5.2 s and shear stress (γ) = 15.5 S^-1, at 41 °C, gave the highest antifungal activity of 65 mm zone of inhibition in the 10 L scale bioreactor compared to the 1L bioreactors (57 mm). These findings have elucidated improved antifungal production by B. subtilis BS20 as well as provided a preliminary data for large scale production.